1. Field of the Invention
The invention relates to a device for comminuting feed material.
2. Description of the Background Art
Such devices belong to the field of mechanical process engineering, in particular the comminution of feed material in the manner of cutting, clipping, tearing, or crushing. But the dissociation of the bond of composite materials, which is always accompanied by a comminution of the feed material, also resides within the scope of the present invention. Generic devices consequently are suitable for the comminution of piece goods and bulk materials, in particular plastics with and without admixtures, wood, waste wood, paper, cardboard, cellulose, textiles, waste material, vulcanized rubber, natural rubber, resins, leather, foodstuffs, semi-luxury foodstuffs, fodder, minerals, pigments, dyes, pharmaceuticals, metals, composite materials such as electronic scrap, cables, used tires, and the like.
The basic principle of material processing is a result of the interaction of rotating cutting, shearing, or tearing tools with stationary tools or else from the impact energy of rapidly rotating striking tools such as hammers, plates, and the like, which crush the feed material. After it has been reduced sufficiently in size, the feed material is removed from the device through a screen, wherein the screen can additionally act as a comminution tool. Thus, the screen functionally subdivides the interior of the housing into an upstream comminution area and a downstream area for discharging the material that has already been comminuted.
In machines of this nature, the attachment of rotating machine parts to stationary machine parts proves to be problematic; in particular the attachment of the rotor to the housing proves to be a critical zone with regard to wear, heat buildup within the device, and quality of the end product.
Mills with a housing having longitudinal walls and transverse walls, in which a rotor extends from one transverse wall to the opposite transverse wall, are generally known. The rotor moving relative to the transverse wall during the course of comminution carries the feed material along in its circular path, which leads to considerable friction at the stationary transverse walls. The consequences are, firstly, wear on the inside of the housing wall and, secondly, an input of heat into the housing itself, since a portion of the supplied drive energy is converted into friction heat. This not only leads to additional thermal loading of the device, with the result that measures may need to be taken for cooling, but also leads to reduced energy efficiency. An example of such a device is disclosed in DE 34 01 929 A1.
In order to counter these problems, it is known to provide, on the faces of the rotor, an annular disk that rotates with the rotor and whose outer circumference extends radially past the comminution tools. The co-rotating annular disk prevents the feed material from coming into direct contact with the housing wall and causing wear and excessive heat there on its circular path. So that the feed material does not jam in the gap between the annular disk and the inside of the housing, the housing wall has a recess concentric to the annular disk into which the rotor extends with its annular disk. In this design, only a small radial annular gap is maintained between the outer circumference of the annular disk and the inner circumference of the recess. Thus, while the problem of wear of the housing inner wall is solved to a great extent in such an embodiment, it has nonetheless become apparent that fine feed material gets into the annular gap between the annular disk and the housing wall, and in this way the annular gap clogs in the course of time. In order to limit frictionally caused wear and heat development in the annular gap, it is necessary to clean it at regular time intervals, with the disadvantage that the expenditure of time required for this purpose increases the downtime of the device.
In order to remedy this problem, US 2006/0118671 A1 proposes forming the concentric recess in the housing walls over the entire thickness of the transverse wall, which is to say to produce a concentric opening in the housing wall within which the rotor is arranged with its rotating annular disk. The radial distance between the annular disk and the housing wall is chosen sufficiently small here that a sealing action arises with respect to the feed material. Nevertheless, during the course of comminution, especially fine particles get into the gap and reemerge on the outside of the housing. In order to capture and remove this material, in accordance with US 2006/0118671 A1 a metal duct is provided on the outside of the housing in the area of the gap.
It proves to be a disadvantage here that the material escaping from the outlet from the seal gap, and hence from the housing, is separated from the remaining flow of material by the transverse wall, and consequently must be recaptured by additional peripheral machine components and delivered to further processing, which entails additional structural and processing costs. From a static perspective, the transverse wall is structurally weakened by the large opening in which the annular disk is located, which impairs the stiffness of the machine construction. The opening also has the result that the rotor cannot be mounted on the transverse walls of the housing, the rotor instead having to be mounted directly on the substratum. The metal ducts attached to the transverse walls are not static load-bearing machine parts such as, e.g., the transverse walls, and consequently cannot be used for mounting the rotor. With regard to cleaning and maintenance that are as fast and effective as possible, the metal ducts on the outsides of the transverse walls only make for additional projections and corners that make such tasks more difficult.